Windows 7 with it's Superbar.Windows Vista with it's complete system change from Windows XP not to mention all the buzz around Windows Longhorn.Windows XP again, major change from 9x kernel to NT kernel. Was really 'slow', horrid 'UI' but we all started liking it after a couple of years and it became the standard.

Seen everything before, and Microsoft are clearly not turning around because of Windows 'Blue'.

All those examples were positive needed changes

7's superbar is greatVista was a very necessary step to 7, all be it one most people want to forget, and it was not a design flaw that killed it, it was the endless number of bugs that did it.XP, again a great change and great OS, being slow to begin with is not a mistake, the UI was fine, although the colour scheme could have been better